Method of preparing a cooled hydrocarbon stream and an apparatus therefor

ABSTRACT

A partially condensed hydrocarbon feed stream is sent to a column. An overhead vapour hydrocarbon stream from the column is then partially condensed by indirect heat exchanging against an expanded cooling fluid flowing through a first section of a cold side heat exchanging channel. The cooling fluid consists of a mixed refrigerant composition, and liquid from the expanded cooling fluid is continuously transformed to vapour thereby forming a residual liquid portion of not evaporated expanded cooling fluid. The residual liquid is used to progressively condense the hydrocarbon feed stream to produce the partially condensed hydrocarbon feed stream that is sent to the column, by allowing the hydrocarbon feed stream to lose heat to the residual liquid passing through a second section of the cold side heat exchanging channel. The liquid component that is condensed out of the overhead vapour hydrocarbon stream is used as reflux for the column.

This application claims the benefit of Indian Application No. 1022/CHE/2012 filed Mar. 20, 2012, which is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a method and apparatus for preparing a cooled hydrocarbon stream from a hydrocarbon feed stream. The cooled hydrocarbon stream may be cooled to such an extent that the hydrocarbon stream is in a fully condensed condition.

BACKGROUND OF THE INVENTION

An example of a hydrocarbon feed stream that in the industry often requires to be cooled is natural gas. Natural gas is a useful fuel source, as well as a source of various hydrocarbon compounds. It is often desirable to liquefy natural gas in a liquefied natural gas (LNG) plant at or near the source of a natural gas stream for a number of reasons. As an example, natural gas can be stored and transported over long distances more readily as a liquid than in gaseous form because it occupies a smaller volume and does not need to be stored at high pressure.

Conventionally, the hydrocarbons heavier than methane are removed as far as needed to produce a liquefied hydrocarbon product stream in accordance within a desired specification. Hydrocarbons heavier than butanes are removed as far as efficiently possible from the natural gas prior to any significant cooling for several reasons, such as having different freezing or liquefaction temperatures that may cause them to block parts of a methane liquefaction plant.

A process and apparatus for cooling a natural gas stream to a fully condensed condition is described in U.S. Pat. No. 6,370,910. The natural gas stream is pre-cooled before it enters into a scrub column. In the scrub column heavier hydrocarbons are withdrawn from the natural gas stream, to obtain a gaseous overhead stream at the top of the scrub column. This gaseous overhead stream is partly condensed by indirect heat exchanging against an (auxiliary) multicomponent refrigerant evaporating at a low (auxiliary) refrigerant pressure in a(n auxiliary) heat exchanger. A condensate stream is separated from the so partly condensed gaseous overhead stream, and returned to an upper part of the scrub column as reflux. The pre-cooling of the natural gas stream is effected by indirect heat exchange with a bleed stream from the multicomponent refrigerant. To this end the bleed stream is passed to a pre-cooling heat exchanger via an expansion valve. The multicomponent refrigerant that has evaporated in the (auxiliary) heat exchanger is removed from the heat exchanger, re-united with the bleed stream that is removed from the pre-cooling heat exchanger, and subsequently recompressed.

The process and apparatus described above has an inherent less than optimal efficiency, because the reflux is produced with the same refrigerant composition and pressure as are used for pre-cooling the natural gas.

SUMMARY OF THE INVENTION

In one aspect, the present invention provides a method of preparing a cooled hydrocarbon stream from a hydrocarbon feed stream, comprising:

-   circulating a cooling fluid consisting of a mixed refrigerant     composition in a loop along a circulation direction wherein, in     consecutive order,

passing the cooling fluid through an expander to provide an expanded cooling fluid,

allowing the expanded cooling fluid to progressively evaporate as the expanded cooling fluid flows through a cold side heat exchanging channel, by allowing the expanded cooling fluid to flow through a first section of the cold side heat exchanging channel in contact with a first cold surface of a first heat exchanging fluid barrier whereby liquid from the expanded cooling fluid is continuously transformed to vapour thereby forming a residual liquid portion of not evaporated expanded cooling fluid, and subsequently allowing the residual liquid portion to continue its flow through a second section of the cold side heat exchanging channel in contact with a second cold surface of a second heat exchanging fluid barrier whereby the residual liquid is continuously vaporized,

compressing the vapour and the vaporized residual liquid to provide a compressed vapour,

transferring heat from the compressed vapour to ambient, and

closing the loop by again passing the cooling fluid through the expander;

-   progressively cooling a hydrocarbon feed stream as it flows through     a second warm section of a warm side heat exchanging channel in     contact with a second warm surface of said second heat exchanging     fluid barrier, thereby forming a pre-cooled hydrocarbon feed stream,     by allowing the hydrocarbon feed stream to lose heat to the     evaporating residual liquid passing through the second section of     the cold side heat exchanging channel; -   passing the pre-cooled hydrocarbon feed stream into a column; -   drawing an overhead vapour hydrocarbon stream from the column; -   progressively condensing the overhead vapour hydrocarbon stream as     it flows through a first warm section of the warm side heat     exchanging channel in contact with a first warm surface of said     first heat exchanging fluid barrier, until the overhead vapour     hydrocarbon stream is partially condensed and forms a partially     condensed hydrocarbon stream, by allowing the overhead vapour     hydrocarbon stream to lose heat to the evaporating expanded cooling     fluid passing through the first section of the cold side heat     exchanging channel; -   separating the partially condensed hydrocarbon stream into a liquid     component and a vaporous component, wherein the vaporous component     comprises the cooled hydrocarbon stream; -   feeding the liquid component into the column as reflux stream.

In another aspect, the present invention provides an apparatus for preparing a cooled hydrocarbon stream from a hydrocarbon feed stream, comprising:

-   a cooling fluid consisting of a mixed refrigerant composition; -   a loop containing the cooling fluid for circulating the cooling     fluid in a circulation direction, which loop, described in     consecutive order in the circulation direction, comprises:

an expander to provide an expanded cooling fluid,

a cold side heat exchanging channel comprising a first section and a second section, wherein the first section is fluidly connected to the expander to receive the expanded cooling fluid, wherein the first section comprises a first heat exchanging fluid barrier with a first cold surface facing into the first section of the cold side heat exchanging channel and arranged to allow passage of the expanded cooling fluid in contact with the first cold surface of the first heat exchanging fluid barrier, and wherein the second section of the cold side heat exchanging channel is arranged to receive at least a residual liquid portion from the first section of the cold side heat exchanging channel, and wherein the second section comprises a second heat exchanging fluid barrier with a second cold surface facing into the second section of the cold side heat exchanging channel and arranged to allow passage of the residual liquid in contact with the second cold surface of the second heat exchanging fluid barrier,

a first compressor train in fluid communication with at least the second section of the cold side heat exchanging channel and comprising at least one first compressor for compressing vaporised expanded cooling fluid and vaporized residual liquid originating from the cold side heat exchanging channel to provide a compressed vapour,

an ambient heat exchanger arranged to receive the compressed vapour and to transfer heat from the compressed vapour to ambient, and

a cooling fluid connection fluidly extending between the ambient heat exchanger and the expander by which the loop is closed;

-   a warm side heat exchanging channel comprising a first warm section     and a second warm section, whereby a first warm surface of said     first heat exchanging fluid barrier faces into the first warm     section, which first warm surface is in heat exchanging contact with     the first cold surface through the first heat exchanging fluid     barrier; and whereby a second warm surface of said second heat     exchanging fluid barrier faces into the second warm section of the     warm side heat exchanging channel, which second warm surface is in     heat exchanging contact with the second cold surface through the     second heat exchanging fluid barrier; -   a hydrocarbon feed stream; -   a source of the hydrocarbon feed stream; -   a column, comprising an overhead discharge outlet, and comprising a     first column inlet and a second column inlet, which column is     fluidly connected to the source of the hydrocarbon feed stream via     the first column inlet and via the second warm section of the warm     side heat exchanging channel to allow passage of the hydrocarbon     feed stream from the source to the column in contact with the second     warm surface; -   a reflux separator comprising a separator inlet and a liquid     discharge outlet and a vapour discharge outlet, whereby said reflux     separator is in fluid communication with the column via the overhead     discharge outlet, the separator inlet and via the first warm section     of the warm side heat exchanging channel to allow passage of an     overhead vapour hydrocarbon stream from the column to the reflux     separator in contact with a first warm surface, whereby said first     warm section of the warm side heat exchanging channel extends     between the overhead discharge outlet and the separator inlet; -   a reflux conduit fluidly connecting the reflux separator and the     column via the liquid discharge outlet and the second column inlet; -   a cooled hydrocarbon stream conduit connected to the vapour     discharge outlet of the reflux separator arranged to remove a     vaporous component from the reflux separator which vaporous     component comprises the cooled hydrocarbon stream.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be further illustrated hereinafter, using non-limiting examples and with reference to the drawing in which;

FIG. 1 represents a schematic process flow scheme representing a method and apparatus according to an embodiment of the invention;

FIG. 2 schematically represents a longitudinal section of a part of a heat exchanger used in FIG. 1;

FIG. 3 represents a schematic process flow scheme representing a method and apparatus for producing a liquefied hydrocarbon stream, such as a liquefied natural gas stream, wherein the embodiment of FIG. 1 is embedded;

FIG. 4 schematically represents an alternative compressor train arrangement that can optionally be used in the embodiment of FIG. 3;

FIG. 5 schematically represents a schematic process flow scheme representing an alternative method and apparatus for producing a liquefied hydrocarbon stream, such as a liquefied natural gas stream, wherein the embodiment of FIG. 1 is embedded;

FIG. 6 schematically represents an alternative heat exchanger arrangement that can optionally be used in the embodiments of FIGS. 1, 3, 4 and 5;

FIG. 7 schematically represents another alternative heat exchanger arrangement that can optionally be used in the embodiments of FIGS. 1, 3, 4 and 5.

In these figures, same reference numbers will be used to refer to same or similar parts. Furthermore, a single reference number will be used to identify a conduit or line as well as the stream conveyed by that line.

DETAILED DESCRIPTION OF THE INVENTION

Described below will be a method and apparatus for preparing a cooled hydrocarbon stream from a hydrocarbon feed stream. The hydrocarbon feed stream is partially condensed. The partially condensed hydrocarbon feed stream is then sent to a column. An overhead vapour hydrocarbon stream from the column is then partially condensed by indirect heat exchanging against an expanded cooling fluid flowing through a first section of a cold side heat exchanging channel. The cooling fluid consists of a mixed refrigerant composition, and liquid from the expanded cooling fluid is continuously transformed to vapour thereby forming a residual liquid portion of not evaporated expanded cooling fluid. The residual liquid is used to progressively condense the hydrocarbon feed stream to produce the partially condensed hydrocarbon feed stream that is sent to the column, by allowing the hydrocarbon feed stream to lose heat to the residual liquid passing through a second section of the cold side heat exchanging channel. The liquid component that is condensed out of the overhead vapour hydrocarbon stream is used as reflux for the column.

Relatively volatile components from the mixed refrigerant composition evaporate in the first section of the cold side heat exchanging channel using heat from the overhead vapour hydrocarbon stream from the column, leaving relatively less volatile components in the residual liquid. This residual liquid is evaporated using heat from the hydrocarbon feed stream. Therefore, the reflux can be at lower temperature than the partially condensed hydrocarbon feed stream being fed to the column, while at the same time optimal use is made of the heat absorbing capacity that is available in the cooling fluid.

Moreover, the composition of the cooling fluid being evaporated in the first section is different from the residual liquid that is evaporated in the second section of the cold side heat exchanging channel, while advantageously no phase separator is necessary to achieve the different compositions.

The cooling fluid can be kept at essentially the same pressure in the first and second sections of the cold side heat exchanging channel, other than dynamic pressure loss inherently caused by passing through the cold side heat exchanger channel and passing from the first section to the second section of the cold side heat exchanger channel. This safes equipment (e.g. an expansion turbine and/or expansion valve) and simplifies re-compression of the evaporated cooling fluid over alternative approaches where the cooling fluid is evaporated at deliberately different pressure levels in the respective first and second sections of the cold side heat exchanging channel. For instance, the residual liquid portion may be passed from the first section of the cold side heat exchanging channel to the second section of the cold side heat exchanging channel without changing the pressure of the residual liquid portion by more than 1 bar anywhere between these first and second sections.

Only one single heat exchanger is required to prepare the cooled hydrocarbon stream. Both the first and second sections of the cold side heat exchanging channel can be located within one single heat exchanger. Being located in a single heat exchanger may mean being located within a single shell.

Referring now to FIG. 1, there is schematically shown an apparatus for preparing a cooled hydrocarbon stream 50 from a hydrocarbon feed stream 10. It comprises a loop in the form of a cooling fluid loop 100 having a circulation direction 101. The cooling fluid loop 100 contains a cooling fluid consisting of a mixed refrigerant composition. The present embodiment uses a so-called tube-in-shell heat exchanger 200, which may be provided in the form of coil-wound heat exchanger.

Described in consecutive order in the circulation direction 101, the cooling fluid loop 100 comprises an expander 110; a cold side heat exchanging channel 120, here as example shown as a shell side of the tube-in-shell heat exchanger 200; a first compressor train 130 in fluid communication with the cold side heat exchanging channel 120; an ambient heat exchanger 140; and a cooling fluid connection 150 fluidly extending between the ambient heat exchanger 140 and the expander 110. Generally, the expander 110 may be provided in any suitable form, for instance an expansion turbine, an expansion valve (such as a Joule Thomson (JT) valve) or a combination thereof. In the example as shown the expander 110 is represented in the form of a JT valve.

In the present embodiment, the cold side heat exchanging channel 120 occupies the entire shell side of the tube-in-shell heat exchanger 200. A bundle break is provided in the tube-in-shell heat exchanger 200, which separates the cold side heat exchanging channel 120 into a first section 124 and a second section 126. The location of the bundle break is schematically indicated by a dashed line 220. In the embodiment as shown, the first section 124 is located gravitationally higher than the second section 126 so that non-evaporated residual liquid of a cooling fluid can traverse the bundle break and flow downward from the first section 124 into the second section 126 by pull of gravity.

The first section 124 of the cold side heat exchanging channel 120 is on an upstream end fluidly connected to the expander 110 and on a downstream end fluidly connected to the second section 126 of the cold side heat exchanging channel 120, via which second section 126 the first section 124 is connected to the first compressor train 130.

Preferably, the cooling fluid loop 100 does not comprise any phase separator between the expander 110 and the second section 126 of the cold side heat exchanging channel 120, when the cooling fluid loop 100 is considered in the circulation direction and in a single pass of the cooling fluid through the cooling fluid loop 100.

A warm side heat exchanging channel 220 is arranged in the heat exchanger, provided with a heat exchanging fluid barrier that a warm side of the heat exchanger from a cold side. In the example, the warm side heat exchanging channel 220 is arranged within the shell 201 of the shell-and-tube heat exchanger 200 as a bundle of tubes traversing the shell side of the shell-and-tube heat exchanger 200. The warm side heat exchanging channel 220 comprises a first warm section 230 and a second warm section 210.

A specific example of a structure of the warm side heat exchanging channel within the shell is illustrated schematically in FIG. 2, wherein a longitudinal cross section is shown though one of the tubes of the tube-in-shell heat exchanger 200. In this example, the first section 124 of the cold side heat exchanging channel 120 comprises a first heat exchanging fluid barrier 231, with a first cold surface 232 facing into the first section 124 of the cold side heat exchanging channel 120. The second section 126 comprises a second heat exchanging fluid barrier 211 with a second cold surface 212 facing into the second section 126 of the cold side heat exchanging channel 120. Likewise the first heat exchanging fluid barrier 231 has a first warm surface 233 that faces into the first warm section 230. The first warm surface 233 faces away from the first cold surface 232, and is in heat exchanging contact with the first cold surface 232 through the first heat exchanging fluid barrier 231. The second heat exchanging fluid barrier 211 has a second warm surface 213 that faces into the second warm section 210 of the warm side heat exchanging channel 220. The second warm surface 213 faces away from the second cold surface 212, and is in heat exchanging contact with the second cold surface 212 through the second heat exchanging fluid barrier 211.

In this case, the first and second heat exchanging fluid barriers (231,211) are formed by the collective tube walls of the relevant tube bundle in the coil-wound heat exchanger. It should be noted that for reason of providing clarity within the drawing the tubes are drawn straight, while in a practical embodiment according to normal design principles known in the art the tube bundle is often arranged spiralling through the shell whereby the tubes within the bundle are spread through the majority of the available cross section within the shell, optionally intertwined with tubes belonging to other tube bundles.

Referring, again, to FIG. 1, the first compressor train 130 comprises at least one first compressor 131, and may optionally comprise a plurality (not shown) of first compressors 131 arranged in a parallel configuration (in which the respective suction inlets of parallel configured first compressors are fluidly connected to each other) and/or in a serial configuration (in which the suction inlet of one of the serially configured first compressor is fluidly connected to the discharge outlet of another one of the serially configured first compressor).

In the embodiment of FIG. 1, the cooling fluid connection 150 that fluidly extends between the ambient heat exchanger 140 and the expander 110 comprises an auxiliary warm side heat exchanging channel 160 arranged in heat exchanging relationship with the cold side heat exchanging channel 120. Similar to the warm side heat exchanging channel 220 described above, the auxiliary warm side heat exchanging channel 160 is arranged in the heat exchanger, and it comprises a third warm section 164 arranged within the second section 126 of the cold side heat exchanging channel 120 and a fourth warm section 166 arranged with in the first section 124 of the cold side heat exchanging channel 120 Like the warm side heat exchanging channel 220, the auxiliary warm side heat exchanging channel 160 may be provided in the form of an auxiliary tube bundle of which tubes are helically arranged within the shell preferably intertwined with the other tubes.

As best viewed in the schematic illustration of FIG. 2, the auxiliary warm side heat exchanging channel 160 comprises a third heat exchanging fluid barrier 161, and a fourth heat exchanging fluid barrier 166. The third heat exchanging fluid barrier 161 has a third surface 162 facing into the second section 126 of the cold side heat exchanging channel 120, and a third warm surface 163 facing into the third warm section 164 of the auxiliary warm side heat exchanging channel 160 and facing away from the third cold surface 162. The third warm surface 163 is in heat exchanging contact with the third cold surface 162 through the third heat exchanging fluid barrier 161. Likewise the fourth heat exchanging fluid barrier 169 has a fourth warm surface 167, which faces into the fourth warm section 166 of the auxiliary warm side heat exchanging channel 160, and which faces away from the fourth cold surface 168. The fourth warm surface 167 is in heat exchanging contact with the fourth cold surface 168 via the fourth heat exchanging fluid barrier 166.

Again with reference to FIG. 1, a source 5 of the hydrocarbon feed stream 10 is in fluid communication with a column 25 via the second warm section 210 of the warm side heat exchanging channel 220. The column 25 comprises an overhead discharge outlet 26, a bottom liquid outlet 22, a first column inlet 21, and a second column inlet 27. The column 25 may optionally be provided with distillation internals, such as a contacting section 28 containing a plurality of gas/liquid contacting trays or structured packing. Preferably, the second column inlet 27 is arranged gravitationally higher than the contacting section 28, as is the overhead discharge outlet 26, whereas the first column inlet 27 is preferably arranged gravitationally lower than the contacting section 28 as is the bottom liquid outlet 22.

The column 25 is fluidly connected to the source 5 of the hydrocarbon feed stream 10 via the first column inlet 21, and via the second warm section 210 of the warm side heat exchanging channel 220 to allow passage of the hydrocarbon feed stream 10 from the source 5 to the column 25 in contact with the second warm surface 213.

A reflux separator 45 is associated with the column 25. The reflux separator 45 comprises a separator inlet 41, a liquid discharge outlet 42 and a vapour discharge outlet 43. The reflux separator 45 is in fluid communication with the column 25 via the overhead discharge outlet 26 of the column 25, the separator inlet 41 and the first warm section 230 of the warm side heat exchanging channel 220 which is located between the overhead discharge outlet 26 of the column 25 and the separator inlet 41. The reflux separator 45 is also in fluid communication with the column 25 via a reflux conduit 47 fluidly connecting the reflux separator 45 and the column 25 via the liquid discharge outlet 42 and the second column inlet 27.

A cooled hydrocarbon stream conduit 50 is fluidly connected to the vapour discharge outlet 43 of the reflux separator 45.

The purpose of the column 25 is to extract heavier hydrocarbons from the hydrocarbon feed stream 10 in the form of the bottom liquid 52 that is removed from the column 25 via the bottom liquid outlet 22. The column 25 may be provided in the form of a distillation column suitable for the purpose, such as an NGL extraction column or a scrub column. The column 25 optimized according to its intended purpose. For instance, if the hydrocarbon feed stream 10 contains methane, and heavier hydrocarbons including C₂-C₄ and C₅+ hydrocarbons, it can be adapted or optimized to extract as much of the C2-C4 components as possible. It may also be adapted or optimized to produce a cooled hydrocarbon stream in cooled hydrocarbon stream conduit 50 that has less than 0.1 mol. % of C₅+ hydrocarbons. In that case the cooled hydrocarbon stream in cooled hydrocarbon stream conduit 50 can ultimately be liquefied without creating solidified hydrocarbon components.

The apparatus of FIG. 1 can be employed as follows in a method of preparing a cooled hydrocarbon stream 50, from a hydrocarbon feed stream 10.

The cooling fluid, consisting of a mixed refrigerant composition, is circulated in a cooling fluid loop 100 along the circulation direction 101. During the circulation, in consecutive order the cooling fluid passes through: the expander 110, the cold side heat exchanging channel 120, the compressor train 130, the ambient heat exchanger 140, and the cooling fluid connection 150 that fluidly extends between the ambient heat exchanger 140 and the expander 110.

The passing the cooling fluid through the expander 110 provides an expanded cooling fluid. The expanded cooling fluid is allowed to progressively evaporate as the expanded cooling fluid flows through the cold side heat exchanging channel 120.

In more detail, expanded cooling fluid is allowed to progressively evaporate by first allowing the expanded cooling fluid to flow through the first section 124 of the cold side heat exchanging channel 120 in contact with the first cold surface 232 of the first heat exchanging fluid barrier 231, whereby liquid from the expanded cooling fluid is continuously transformed to vapour. Hereby, a residual liquid portion of not evaporated expanded cooling fluid is formed. Subsequently, the residual liquid portion is allowed to continue its flow through the cold side heat exchanging channel 120 through the second section 126 thereof, and in contact with the second cold surface 212 of the second heat exchanging fluid barrier 211 whereby the residual liquid is continuously vaporized.

Preferably, during any single pass of the cooling fluid through the cooling fluid loop 100, the expanded cooling fluid does not pass through any phase separator between the expander 110 and the second section 126 of the cold side heat exchanging channel 120.

In the next part of the circulating of the cooling fluid, the vapour and the vaporized residual liquid (in discharge line 128) are compressed as a combined vapour, thereby providing a compressed vapour. In the embodiment of FIG. 1, the vapour is allowed to flow from the first section 124 to and through the second section 126 of the cold side heat exchanging channel 120. Thus the vaporized residual liquid is mixed with the vapour from the first section 124 already in the heat exchanger. Alternatives are possible. For instance, the vapour could be removed from the heat exchanger separately from the vaporised residual liquid, and then combined to form a combined vapour that can be fed to the compressor train 130 as a single stream. Still alternatively, the separately removed vapour and vaporized residual liquid can be separately compressed and brought together somewhere else in the cooling fluid loop 100.

Next, heat is transferred from the compressed vapour to ambient thereby producing an ambient cooled compressed cooling fluid. The heat comprises heat added during compression as well as heat gained while passing through the cold side heat exchanging channel 120 and being evaporated therein. The loop is closed by again passing the cooling fluid through the expander 110.

Optionally, but preferably, during passing of the compressed vapour (in the form of the ambient cooled compressed cooling fluid) from the ambient heat exchanger 140 to the expander 110, the compressed vapour flows through the optional auxiliary warm side heat exchanging channel 160. This comprises flowing through the third warm section 164 in contact with the third warm surface 162 of the third heat exchanging fluid barrier 161 and subsequently through the fourth warm section 166 in contact with the fourth warm surface 167 of the fourth heat exchanging fluid barrier 169. The cooling fluid in the cold side heat exchanging channel 120 is in contact with the respective fourth (168) and third (162) cold surfaces. Thereby, the compressed vapour can lose heat to the evaporating residual liquid passing through the second section 126 of the cold side heat exchanging channel 120 and subsequently to the evaporating expanded cooling fluid passing through the first section 124 of the cold side heat exchanging channel 120. By these losses of heat, the compressed vapour can condense and in so far as it has already condensed it can be subcooled prior to being expanded in the expander 110.

The hydrocarbon feed stream 10 is progressively cooled as it flows through the second warm section 210 of the warm side heat exchanging channel 220 in contact with the second warm surface 213 of the second heat exchanging fluid barrier 211. Herewith a pre-cooled hydrocarbon feed stream 20 is formed, by allowing the hydrocarbon feed stream 10 to lose heat to the evaporating residual liquid passing through the second section 126 of the cold side heat exchanging channel 120 in contact with the second cold surface 212 of the second heat exchanging fluid barrier 211. The pre-cooled hydrocarbon feed stream 20 preferably consists of a mixture of vapour and liquid phases.

The thus pre-cooled hydrocarbon feed stream 20 is then removed from the heat exchanger and passed into the column 25, suitably via the first column inlet 21. An overhead vapour hydrocarbon stream 30 is drawn from the column 25 and passed back to the heat exchanger. Here the overhead vapour hydrocarbon stream 30 is progressively condensed as it flows through the first warm section 230 of the warm side heat exchanging channel 220 in contact with the first warm surface 233 of the first heat exchanging fluid barrier 231. The overhead vapour hydrocarbon stream 30 is partially condensed by allowing the overhead vapour hydrocarbon stream 30 to lose heat to the evaporating expanded cooling fluid passing through the first section 124 of the cold side heat exchanging channel 126 in contact with the first cold surface 232 of the first heat exchanging fluid barrier 231. Hereby a partially condensed hydrocarbon stream 40 is formed out of the overhead vapour hydrocarbon stream 30.

The partially condensed hydrocarbon stream 40 is passed into the reflux separator 45, suitably via the separator inlet 41, in which reflux separator 45 the partially condensed hydrocarbon stream 40 is phase separated into a liquid component and a vaporous component. The vaporous component, which comprises the cooled hydrocarbon stream, is discharged via the vapour discharge outlet 43 into the cooled hydrocarbon stream conduit 50. The liquid component is discharged via the liquid discharge outlet 42 into the reflux conduit 47 and passed to and fed as reflux stream into the column 25. This may be done for instance by force of gravity and/or with assistance of a reflux pump (not shown).

Interestingly, the temperature gradient in the column 25 is determined by the mixed refrigerant composition as the mixed refrigerant composition determines the temperature profile within the heat exchanger 200.

The hydrocarbon feed stream 10 to be cooled, and ultimately preferably liquefied as will be described in embodiments below, may be derived from any suitable gas stream to be refrigerated and optionally liquefied. An often used example is a natural gas stream, for instance obtained from natural gas or petroleum reservoirs, shale, or coal beds. As an alternative the hydrocarbon feed stream 10 may also be obtained from another source, including as an example a synthetic source such as a Fischer-Tropsch process.

When the hydrocarbon feed stream 10 is a natural gas stream, it is usually comprised substantially of methane. Preferably the hydrocarbon feed stream 10 comprises at least 50 mol % methane, more preferably at least 80 mol % methane.

Depending on the source, natural gas may contain varying amounts of hydrocarbons heavier than methane such as in particular ethane, propane and the butanes (together indicated by the abbreviation C₂-C₄), and possibly lesser amounts of pentanes and aromatic hydrocarbons (C₅₊ hydrocarbons). The composition varies depending upon the type and location of the gas.

The column 25 in the present invention suitably serves to extract such C₅+ hydrocarbons so as to produce a cooled hydrocarbon stream in cooled hydrocarbon stream conduit 50 that has less than 0.1 mol. % of these C₅₊ hydrocarbons. Moreover, natural gas liquids consisting mainly of C₂-C₄, hydrocarbons, particularly petroleum gas liquids in the form of C₃-C₄ hydrocarbons (LPG) are typically recovered as well.

The natural gas may also contain non-hydrocarbons such as H₂O, N₂, CO₂, Hg, H₂S and other sulphur compounds, and the like. Thus, if desired, the source 5 of the hydrocarbon feed stream 10 may comprise equipment to perform pre-treatment steps comprising one or more of reduction and/or removal of undesired components such as CO₂ and H₂S or other steps such as early cooling, pre-pressurizing or the like. As these steps are well known to the person skilled in the art, their mechanisms are not further discussed here. As part of such pre-treatment, the natural gas may be dried in accordance with WO 2012/000998, which disclosure is incorporated herein by reference.

Reference is now made to FIG. 3, which schematically illustrates a method and apparatus for producing a liquefied hydrocarbon stream 90, such as a liquefied natural gas stream, wherein the invention as described above is embedded. In addition to the elements described hereinabove, such as the cooling fluid loop 100 and the heat exchanger 200, the method and apparatus for producing the liquefied hydrocarbon stream 90 in accordance with FIG. 3 further comprises a main refrigeration loop 300 comprising a main cooling fluid. The main cooling fluid consists of a main mixed refrigerant composition, that is different from the mixed refrigerant composition described above in that it contains relatively more volatile constituents. The main refrigeration loop 300 in this embodiment is separate from the cooling fluid loop 100 in which the cooling fluid is circulated as described above. This means that under normal circulation within the respective loops, the cooling fluid and the main cooling fluid are kept separated from each other.

Described in consecutive order in a circulation direction 301 of the main refrigeration loop 300, the main refrigeration loop 300 comprises one or more expanders 310 a, 310 b here as example shown in the form of expansion valves; a main cryogenic heat exchanger 400; a second compressor train 330 in fluid communication with the main cryogenic heat exchanger 400; a main ambient heat exchanger 340; and a main cooling fluid connection 350 fluidly extending between the main ambient heat exchanger 340 and the one or more expanders 310 a, 310 b.

In the embodiment as shown the main cooling fluid connection 350 passes through the shell-in-tube heat exchanger 200 of the cooling fluid loop 100 via a second auxiliary warm side heat exchanging channel 360 extending through the shell side of the shell-in-tube heat exchanger 200 similar to the auxiliary warm side heat exchanging channel 160. From there the second auxiliary warm side heat exchanging channel 360 is connected to the main cryogenic heat exchanger 400 via a main cooling fluid separator 365 wherein the main cooling fluid can be separated in a light mixed refrigerant stream 370 a to be discharged from the top of the main cooling fluid separator 365 and a heavy mixed refrigerant stream 370 b to be discharged from the bottom of the main cooling fluid separator 365. However, alternative main liquefaction processes and line ups exist which may be employed if desired.

The second compressor train 330 comprises at least one second compressor. In the embodiment as shown in FIG. 3 the at least second compressor is provided in the form of an LP compressor 331 in a first casing and an MP/HP compressor 333 combined as two successive stages in a second casing being a separate casing from the first casing. The LP compressor 331 discharges into the suction inlet of the MP/HP compressor 333 via a first ambient intercooler 332. A second ambient intercooler 334 may be provided between the MP and HP stages in the MP/HP compressor 333. Alternative compressor trains can be selected instead of the specific embodiment described here.

The cooled hydrocarbon stream conduit 50 connects to a liquefaction passage 55 extending through the main cryogenic heat exchanger 400. The liquefaction passage 55 extends through the main cryogenic heat exchanger 400 in heat exchanging contact with the main cooling fluid that has been expanded in the one or more expanders 310 a, 310 b and fed to the main cryogenic heat exchanger 400. By indirectly heat exchanging the cooled hydrocarbon stream 50 against the main cooling fluid that is evaporating, the cooled hydrocarbon stream is liquefied and preferably subcooled and thus converted into a raw liquefied hydrocarbon product 60.

The raw liquefied hydrocarbon product 60 may be further treated by end treatment system 80 to yield for instance the liquefied hydrocarbon stream 90 and a by-product stream 70. Such by-product stream may be in vapour phase and it could be end compressed to a desired pressure in an end compressor 85 and subsequently heat exchanged against the ambient in end heat exchanger 86. Usually the by-product stream 70 has a much lower temperature than the cooled hydrocarbon stream in cooled hydrocarbon stream conduit 50. In such as case, preferred embodiment embodiments provide for cold recovery. One suitable way is by indirectly heat exchanging the by-product stream 70 before any end compression against a slipstream of the light mixed refrigerant stream 370 a which is split off between the main cooling fluid separator 365 and the main cryogenic heat exchanger 400 and indirectly heat exchanged with the by-product stream 70 instead of in the evaporating main cooling fluid main cryogenic heat exchanger 400. Another suitable way is by indirectly heat exchanging the by-product stream 70 before any end compression against a slipstream of the cooled hydrocarbon stream which is split off from the cooled hydrocarbon stream conduit 50 between the reflux separator 45 and the liquefaction passage 55 in the main cryogenic heat exchanger 400 and is and indirectly heat exchanged with the by-product stream 70 instead of the evaporating main cooling fluid in the main cryogenic heat exchanger 400.

In a typical liquefaction plant, the end treatment system 80 contains one or more expanders to depressurize the raw liquefied hydrocarbon product 60. The by-product stream 70 may suitably contain flash vapours that are generated by such depressurization. The end treatment system may be selected with the aim to bring the liquefied hydrocarbon stream within a maximum specified content of light contaminants such as nitrogen and helium in the case the liquefied hydrocarbon stream consists of LNG. Numerous suitable end treatment systems are known in the art and the present invention is not limited to any one specific selection of end treatment system.

In the embodiment of FIG. 3, the compressing of the vapour and the vaporized residual liquid is performed with the first compressor train 130 comprising at least the one first compressor 131, while the circulating of the main cooling fluid comprises compressing the main cooling fluid in the second compressor train comprising the at least one second compressor (331,333). Each of the compressors in the first compressor train 130 and of the second compressor train 330 may be provided with its own dedicated one or more compressor drivers. Suitable drivers include a steam turbine, a gas turbine (industrial frame type or, preferably, of aero derivative type), an electric motor. Sets comprising several suitable drivers in combination may be employed. Several of the compressors may be jointly driven by one or more combined drivers. For instance, the LP and MP/HP compressors 331,333 may be jointly driven by one set of one or more drivers, whereas the at least one first compressor 131 of the first compressor train 130 may be driven by another set of one or more drivers. Another option is to employ one set of drivers to drive every compressor of the first compressor train 130 and a subset of compressors of the second compressor train 330 or the other way round. This option offers advantages in terms of load balancing between the two separate cooling fluid loops.

FIG. 4 illustrates a special case wherein all compressors (131) of the first compressor train 130 are jointly driven together with all compressors (331,333) of the second compressor train 330 by one single set 335 of drivers. The single set 335 of drivers may consist of a single gas turbine or a single steam turbine or a single electric motor, or any combination thereof. In this special case, a common drive shaft 336 mechanically drives the at least one first compressor and any other compressor in the first compressor train 130 as well as the at least one second compressor and any other compressor in the second compressor train 330.

TABLE 1 Reference numbers correspond to FIG. 3. Ref. 10 20 30 40 47 50 52 60 70 90 Physical conditions Phase V V + L V V + L V + L V V L V L (V/L) Flow rate 2.69 2.69 2.68 2.68 0.09 2.59 0.11 2.59 0.15 2.43 (kmol/s) Temp (° C.) 37 −6 −10 −23 −23 −23 −6 −153 −161 −161 Pressure 58 56 50 53 56 53 56 47 1.1 5.0 (bara) Composition (mol. %) N2 0.83 0.83 0.84 0.84 0.13 0.86 0.11 0.86 9.2 0.34 C1 88.0 88.0 88.5 88.5 40.8 90.1 34.2 90.1 90.8 90.1 C2 5.6 5.6 5.6 5.6 12.4 5.4 9.8 5.4 0.01 5.7 C3 2.7 2.7 2.7 2.7 16.9 2.3 13.1 2.3 0.00 2.4 C4 (i + n) 2.2 2.2 2.2 2.2 27.6 1.3 23.5 1.3 0.00 1.4 C5+ 0.7 0.7 0.11 0.11 2.3 0.04 19.3 0.04 0.00 0.04

Table 1 shows physical conditions and compositions of the hydrocarbon stream in the process of FIG. 3 as calculated for an example hydrocarbon feed gas using heat and material balance software. For this example, the mixed refrigerant composition of the cooling fluid is (in mol. %) 1.0 of methane, 48.2 of ethylene, 4.2 of propane, 16.6 of butanes; the main mixed refrigerant composition of the main cooling fluid is (in mol. %) 6.5 of nitrogen, 34.7 of methane, 40.2 of ethylene, 14.2 of propane, 4.4 of butanes. The amount of CO₂ in the hydrocarbon feed stream 10 was less than 50 ppm (by mol) which could be achieved by applying a CO₂ removal process in a pre-treatment.

The embodiment of FIG. 4 shows how the invention can be embedded in a so-called double mixed refrigerant (DMR) process. FIG. 5 is an example wherein the invention is embedded in a so-called single mixed refrigerant (SMR) process. In this case a combined ambient heat exchanger 540 fulfils the functions of both the ambient heat exchanger 140 and the main ambient heat exchanger 340 of FIG. 1. Between the combined ambient heat exchanger 540 and the various expanders 110, 310 a, 310 b a cooling fluid separator 560 is provided that discharged into the main cooling fluid connection 350 and the cooling fluid connection 150. A combined SMR compressor train 530 fulfils the function of the first (130) and second (330) compressor trains described above. As shown, an SMR MP/HP compressor 533 corresponds to the first compressor train 130 of FIG. 3 while an SMR LP compressor 531 together with the SMR MP/HP compressor 533 corresponds to the second compressor train 330 of FIG. 3. Similar to the LP compressor 331 and the MP/HP compressor 333 of FIG. 3, the SMR LP compressor 531 discharges into the suction inlet of the SMR MP/HP compressor 533 via a first SMR ambient intercooler 532. A second SMR ambient intercooler 534 may be provided between the MP and HP stages in the SMR MP/HP compressor 533. Alternative compressor train configurations can be selected instead of the specific embodiment described here.

In the embodiments described above, the first heat exchanging fluid barrier 231 and the second heat exchanging fluid barrier 211 are both located within a single heat exchanger 200. Advantageously, the residual liquid portion is passed from the first section 124 of the cold side heat exchanging channel 120 to the second section 126 of the cold side heat exchanging channel 120 without changing the pressure of the residual liquid portion by more than 1 bar anywhere between these first (124) and second sections (126). This is easily attainable by arranging the first (124) and second (126) sections of the cold side heat exchanging channel 120 within a single shell of a single heat exchanger. An important advantage is that the compressor train 130 can be kept simple because it does not have to handle multiple input vapour streams at mutually different pressure levels.

Furthermore, the residual liquid portion is advantageously passed from the first section 124 of the cold side heat exchanging channel 120 to the second section 126 of the cold side heat exchanging channel 120 without changing the composition of the residual liquid portion anywhere between these first (124) and second sections (126). This has as advantage that a minimum of equipment is needed if the composition does not need to be changed. Finally, the residual liquid portion is passed from the first section 124 of the cold side heat exchanging channel 120 to the second section 126 of the cold side heat exchanging channel 120 without changing the flow rate of the residual liquid portion anywhere between these first (124) and second sections (126).

While these conditions can easily be met using a single heat exchanger, for completeness, FIGS. 6 and 7 show alternative embodiments wherein the first warm section 230 (comprising the first heat exchanging fluid barrier) is located within a first heat exchanger 200A and the second warm section 210 (comprising the second heat exchanging fluid barrier) is located within a second heat exchanger 200B. The first (200A) and second (220B) heat exchangers are interconnected to allow fluid communication between the first (124) and second (126) sections of the cold side heat exchanging channel 120. In the case of FIG. 6, only the residual liquid portion 129, which is separated off in phase separator 127 from the vapour that consists of the evaporated expanded cooling fluid, is conveyed from the first heat exchanger 200A to the second heat exchanger 200B. The vapour 128 a from the first heat exchanger 200A and the vaporized residual liquid 128 b from the second heat exchanger 200B are combined before compressing in the compressor train 130.

An advantage of the embodiment of FIGS. 6 and 7 is that it may be easier to connect the warm side heat exchanging channel 220 to the column 25. However, a disadvantage of the embodiment of FIG. 6 is that the interconnection that allows fluid communication between the first and second sections of the cold side heat exchanging channel may cause an additional pressure drop on the cooling fluid.

In an alternative embodiment, the cooling fluid loop 100 does not comprises any phase separator between the first section 124 and the second section 126 of the cold side heat exchanging channel 120, when the cooling fluid loop 100 is considered in the circulation direction and in any single pass of the cooling fluid through the cooling fluid loop 100.

In FIG. 7 the first and second heat exchangers (200A, 200B) are provided in the form of plate-fin type heat exchangers. An advantage is that the phase separator 127 of the embodiment of FIG. 6 can suitably be avoided, as it is less challenging to convey the vapour and residual liquid portion from the first heat exchanger 200A to the second heat exchanger 200B as a two-phase fluid in the case of plate-fin type heat exchangers than in the case of tube-in-shell type heat exchangers. 

What is claimed is:
 1. A method of preparing a cooled hydrocarbon stream from a hydrocarbon feed stream, comprising: circulating a cooling fluid consisting of a mixed refrigerant composition in a loop along a circulation direction wherein, in consecutive order, passing the cooling fluid through an expander to provide an expanded cooling fluid, allowing the expanded cooling fluid to progressively evaporate as the expanded cooling fluid flows through a cold side heat exchanging channel, by allowing the expanded cooling fluid to flow through a first section of the cold side heat exchanging channel in contact with a first cold surface of a first heat exchanging fluid barrier whereby liquid from the expanded cooling fluid is continuously transformed to vapour thereby forming a residual liquid portion of not evaporated expanded cooling fluid, and subsequently allowing the residual liquid portion to continue its flow through a second section of the cold side heat exchanging channel in contact with a second cold surface of a second heat exchanging fluid barrier whereby the residual liquid is continuously vaporized, compressing the vapour and the vaporized residual liquid to provide a compressed vapour, transferring heat from the compressed vapour to ambient, and closing the loop by again passing the cooling fluid through the expander; progressively cooling a hydrocarbon feed stream as it flows through a second warm section of a warm side heat exchanging channel in contact with a second warm surface of said second heat exchanging fluid barrier, thereby forming a pre-cooled hydrocarbon feed stream consisting of a mixture of vapour and liquid phases, by allowing the hydrocarbon feed stream to lose heat to the evaporating residual liquid passing through the second section of the cold side heat exchanging channel; passing the pre-cooled hydrocarbon feed stream into a column; drawing an overhead vapour hydrocarbon stream from the column; progressively condensing the overhead vapour hydrocarbon stream as it flows through a first warm section of the warm side heat exchanging channel in contact with a first warm surface of said first heat exchanging fluid barrier, until the overhead vapour hydrocarbon stream is partially condensed and forms a partially condensed hydrocarbon stream, by allowing the overhead vapour hydrocarbon stream to lose heat to the evaporating expanded cooling fluid passing through the first section of the cold side heat exchanging channel; separating the partially condensed hydrocarbon stream into a liquid component and a vaporous component, wherein the vaporous component comprises the cooled hydrocarbon stream; feeding the liquid component into the column as reflux stream.
 2. The method of claim 1, wherein the first heat exchanging fluid barrier and the second heat exchanging fluid barrier are both located within a single heat exchanger.
 3. The method of claim 1, wherein the first warm section, comprising the first heat exchanging fluid barrier, is located within a first heat exchanger and the second warm section, comprising the second heat exchanging fluid barrier, is located within a second heat exchanger, wherein the first heat exchanger is fluidly interconnected with the second heat exchanger to allow fluid communication from the first section to the second section of the cold side heat exchanging channel.
 4. The method of claim 3, wherein the residual liquid portion is passed from the first section of the cold side heat exchanging channel to the second section of the cold side heat exchanging channel without changing the pressure of the residual liquid portion by more than 1 bar anywhere between these first and second sections.
 5. The method of claim 3, wherein the residual liquid portion is passed from the first section of the cold side heat exchanging channel to the second section of the cold side heat exchanging channel without changing the composition of the residual liquid portion anywhere between these first and second sections.
 6. The method of claim 3, wherein the residual liquid portion is passed from the first section of the cold side heat exchanging channel to the second section of the cold side heat exchanging channel without changing the flow rate of the residual liquid portion anywhere between these first and second sections.
 7. The method of claim 3, wherein during any single pass of cooling fluid through the loop the cooling fluid does not pass through any phase separator between the expander and the second section of the cold side heat exchanging channel.
 8. The method of claim 1, wherein during any single pass of cooling fluid through the loop the cooling fluid does not pass through any phase separator between the expander and the second section of the cold side heat exchanging channel.
 9. The method of claim 1, further comprising, between said transferring of heat from the compressed vapour to ambient and said closing the loop by again passing the cooling fluid through the expander, progressively cooling the compressed vapour as it flows through an auxiliary warm side heat exchanging channel, whereby flowing through the auxiliary warm side heat exchanging channel comprises: flowing through a third warm section in contact with a third warm surface of a third heat exchanging fluid barrier, by allowing the compressed vapour to lose heat to the evaporating residual liquid passing through the second section of the cold side heat exchanging channel and subsequently flowing through a fourth warm section in contact with a fourth warm surface of a fourth heat exchanging fluid barrier, by allowing the compressed vapour having passed through the third warm section to lose heat to the evaporating expanded cooling fluid passing through the first section of the cold side heat exchanging channel.
 10. The method of claim 1, further comprising indirectly heat exchanging the vaporous component from the partially condensed hydrocarbon stream against an evaporating main cooling fluid.
 11. The method of claim 10, further comprising circulating the main cooling fluid in a main refrigeration loop, wherein the main refrigeration loop is separate from the loop in which the cooling fluid is circulated.
 12. The method of claim 11, wherein said compressing of the vapour and the vaporized residual liquid is performed with a first compressor train comprising at least one first compressor, and wherein said circulating of the main cooling fluid comprises compressing the main cooling fluid in a second compressor train comprising at least one second compressor and, further wherein a common drive shaft mechanically drives the at least one first compressor and any other compressor in the first compressor train as well as the at least one second compressor and any other compressor in the second compressor train.
 13. The method of claim 1, wherein the hydrocarbon feed stream comprises natural gas and wherein the cooled hydrocarbon stream is a liquefied natural gas stream.
 14. An apparatus for preparing a cooled hydrocarbon stream from a hydrocarbon feed stream, comprising: a cooling fluid consisting of a mixed refrigerant composition; a loop containing the cooling fluid for circulating the cooling fluid in a circulation direction, which loop, described in consecutive order in the circulation direction, comprises: an expander to provide an expanded cooling fluid, a cold side heat exchanging channel comprising a first section and a second section, wherein the first section is fluidly connected to the expander to receive the expanded cooling fluid, wherein the first section comprises a first heat exchanging fluid barrier with a first cold surface facing into the first section of the cold side heat exchanging channel and arranged to allow passage of the expanded cooling fluid in contact with the first cold surface of the first heat exchanging fluid barrier, and wherein the second section of the cold side heat exchanging channel is arranged to receive at least a residual liquid portion from the first section of the cold side heat exchanging channel, and wherein the second section comprises a second heat exchanging fluid barrier with a second cold surface facing into the second section of the cold side heat exchanging channel and arranged to allow passage of the residual liquid in contact with the second cold surface of the second heat exchanging fluid barrier, a first compressor train in fluid communication with at least the second section of the cold side heat exchanging channel and comprising at least one first compressor for compressing vaporised expanded cooling fluid and vaporized residual liquid originating from the cold side heat exchanging channel to provide a compressed vapour, an ambient heat exchanger arranged to receive the compressed vapour and to transfer heat from the compressed vapour to ambient, and a cooling fluid connection fluidly extending between the ambient heat exchanger and the expander by which the loop is closed; a warm side heat exchanging channel comprising a first warm section and a second warm section, whereby a first warm surface of said first heat exchanging fluid barrier faces into the first warm section, which first warm surface is in heat exchanging contact with the first cold surface through the first heat exchanging fluid barrier; and whereby a second warm surface of said second heat exchanging fluid barrier faces into the second warm section of the warm side heat exchanging channel, which second warm surface is in heat exchanging contact with the second cold surface through the second heat exchanging fluid barrier; a hydrocarbon feed stream; a source of the hydrocarbon feed stream; a column, comprising an overhead discharge outlet, and comprising a first column inlet and a second column inlet, which column is fluidly connected to the source of the hydrocarbon feed stream via the first column inlet and via the second warm section of the warm side heat exchanging channel to allow passage of the hydrocarbon feed stream from the source to the column in contact with the second warm surface whereby forming a pre-cooled hydrocarbon feed stream consisting of a mixture of vapour and liquid phases; a reflux separator comprising a separator inlet and a liquid discharge outlet and a vapour discharge outlet, whereby said reflux separator is in fluid communication with the column via the overhead discharge outlet, the separator inlet and via the first warm section of the warm side heat exchanging channel to allow passage of an overhead vapour hydrocarbon stream from the column to the reflux separator in contact with a first warm surface, whereby said first warm section of the warm side heat exchanging channel extends between the overhead discharge outlet and the separator inlet; a reflux conduit fluidly connecting the reflux separator and the column via the liquid discharge outlet and the second column inlet; a cooled hydrocarbon stream conduit connected to the vapour discharge outlet of the reflux separator arranged to remove a vaporous component from the reflux separator which vaporous component comprises the cooled hydrocarbon stream.
 15. The apparatus of claim 14, wherein the first heat exchanging fluid barrier and the second heat exchanging fluid barrier are both located within a single heat exchanger.
 16. The apparatus of claim 14, wherein the first warm section, comprising the first heat exchanging fluid barrier, is located within a first heat exchanger and the second warm section, comprising the second heat exchanging fluid barrier, is located within a second heat exchanger, wherein the first heat exchanger is fluidly interconnected with the second heat exchanger to allow fluid communication from the first section to the second section of the cold side heat exchanging channel.
 17. The apparatus of claim 16, wherein the loop does not comprise any phase separator between the expander and the second section of the cold side heat exchanging channel when the loop is considered in a circulation direction and in a single pass.
 18. The apparatus of claim 14, wherein the loop does not comprise any phase separator between the expander and the second section of the cold side heat exchanging channel when the loop is considered in a circulation direction and in a single pass. 